Thermostatic bimetal

ABSTRACT

A THERMOSTATIC BIMETAL HAVING ENHANCED TEMPERATURE DEPENDENT CHARACTERISTICS SUCH AS THE AMOUNT AND LINEARITY OF DEFLECTION AND DEVELOPED FORCE AS WELL AS AN EXTENDED TEMPERATURE RANGE OF MAXIMUM SENSITIVITY. THE BIMETAL EMPLOYS A LOW EXPANDING COMPONENT CONTAINING, AS MAJOR CONSTITUENT, 30.75%-31.75% BY WEIGHT OF NICKEL, 6.5%8.5% OF COBALT, BALANCE IRON. THIS COMPONENT CAN ALSO   CONTAIN, AS MINOR CONSTITUENTS, MANGANESE, CARBON AND SILICON.

June l, 1971 A, GOTTUEB ETAL 3,581,366

THERMOSTATIG BIMETAL Filed Dec. 9, 1968 .fda

ATTORNEY United States Patent O 3,581,366 THERMOSTATIC BIMETAL ArnoldGottlieb, Colonia, and George A. Maiesko, Glen Ridge, NJ., assgnors toWilbur B. Driver Company Filed Dec. 9, 1968, Ser. No. 782,070 Int. ICl.B32b 15/00 U.S. Cl. 29-195.S 2 Claims ABSTRACT F THE DISCLOSURE Athermostatic bimetal having enhanced temperature dependentcharacteristics such as the amount and linearity of deflection anddeveloped force as Well as an extended temperature range of maximumsensitivity. The bimetal employs a low expanding component containing,as major constituents, 30.75 %31.75 by weight of nickel, 6.5%- 8.5% ofcobalt, balance iron. This component can also contain, as minorconstituents, manganese, carbon and silicon.

SUMMARY OF THE INVENTION All thermostatic bimetals possess certainimportant characteristics which are functions of temperature; i.e., theamount and linearity of deflection, the amount and linearity ofdeveloped force, and the range of maximum sensitivity. (This range isthe temperature range of maximum rate of change of deflection andforce.) All of these characteristics are related to Aa, which is thediierence between the coeflicients of thermal expansion of the high andthe low expanding components of the bimetal. The standard low expandingcomponent is Invar, which uses two major constituents, nickel (36% byweight) and iron.

In contradistinction, We employ as a low expanding component aniron-nickel-cobalt alloy having the following composition, by weight:

Percent Nickel 30.75-31.75 Cobalt 6.5-8.5 Iron Balance In addition, thisalloy can contain 0.05%0.50% of manganese and .015%0.12% of carbon.Further, this alloy can also contain .015%-0.15% of silicon. The Aaattained from thermostatic bimetals using this alloy is larger than anyother bimetals using Invar and moreover, the linearity of Aa ismaintained within desired limits over a greater temperature range. As aresult, our bimetal, for a given temperature range, is characterized byenhanced magnitude and linearity of both force and deflection as well asan extended range of maximum sensitivity.

BRIEF DESCRIPTION OF THE DRAWINGS In the drawings:

FIG. 1 is a perspective View of a bimetal in accordance with ourinvention; and

FIG. 2 is a graph comparing 4the change of Aa with ternperature ofcertain of our bimetals as compared to a bimetal using Invar.

DETAILED DESCRIPTION OF PREFERRED EMBODIMENT FIG. 1 shows a typicalbimetal in accordance with our invention having two bonded layers and12. Layer 10 is a conventional high expanding component such aschromium-nickel-iron. Layer 12 is a low expanding component inaccordance with our invention.

The overall composition ranges of the major constitu- 3,581,366 PatentedJune l, 1971 ents of this low expanding component as expressed inpercent by weight are:

The ranges of the minor constituents of this component are:

Percent Manganese 0.05-0.50 Carbon 0.015-0.12 Silicon 0.0150.15

No special processing is required in using this alloy together withother bimetal alloys as compared to using standard Invar. Conventionalhot and cold bonding techniques may be used together with standardannealing and cold rolling procedures.

The important thermostatic bimetal characteristics of curvature(reciprocal of radius of curvature), deection and force are functions ofAa (the difference in expansion coeicients of the high and low expandingelements), as Well as the thicknesses of these components and the ratioof the elastic moduli of the low expanding and high expandingcomponents. Since the modulus of our low expanding alloy isapproximately the same as that of standand Invar and the thickness is adesign consideration only, Aa is the most important parameter.

A known bimetal using Invar as the low expanding component and a knownnickel-chromium-iron high eX- panding component (typical composition 22%by weight of chromium, 3% nickel, balance iron) was prepared, and its Aawas measured and plotted as a function of temperature as shown at curve20 in FIG. 2.

Two rbimetals using the same high expanding component and two differentcompositions of our low expanding alloy were prepared and the twodifferent Aas were measured and plotted as a function of temperature asShown at curves 22 and 24 respectively in FIG. 2.

The low expanding alloy used in obtaining curve 22 had the followingcomposition:

Nickel 31.29

Cobalt 7.05 Manganese 0.10 Carbon 0.03 7

Silicon 0.10

The low expanding alloy used in obtaining curve 24 had the followingcomposition:

Nickel 31.54 Cobalt 8.16 Manganese 0.07 Carbon 0.016 Silicon 0.10

It can be seen that the Aa for each of curves 22 and 24 is not onlylarger `than that for curve 20, Ibut is also more nearly constant withincreasing temperature. Note that curves 22 and 24 have a spread in Aixof .50X 10H6/ F. and .20 l06/ F. respectively as compared to a spread of.90X106/ F. for curve 20 over the temperature range of 10W-500 F.

The flexivity coecient is a fundamental parameter for evaluating bimetalcharacteristics. It is the temperature coefficient of curvature denedas:

e-at F: R. R1

where:

F=Flexivity R1=Radius of curvature at temperature T1 R2=Radius ofcurvature at temperature T2 t=Thickness of bimetal The following tablecompares the flexivity coeicients that can be obtained with Ithecompositions such as used for curves 22 and '24 as compared with theknown composition of curve 20. The temperature range for flexivitymeasurement is 100 F.300 F. and the two components have equalthicknesses.

FLEXIVITIES [Parts per million per degree E] Over the temperature rangeof 100 F.-300 F.

Curve 20 14.6 Curve 22 15.7, Curve 24 15.3

Greater increases in flexivity can be obtained when high expandingelements having lower expansion coefficients than that used herein arecoupled without low expanding alloy.

As a result, our bimetals, as compared to known bi- -metals, arecharacterized by:

Within the normal operating temperature range of bimetals, thecomposition ranges given herein result in the optimization of Aa and thetemperature range of maximum sensitivity.

While we have described our invention with particular reference topreferred embodiments, our protection is to be limited only yby thescope of the claims which follow.

What is claimed is: 1. A thermostatic bimetal comprising: rst and secondmetallic layers bonded together tol deine a strip, the rst layer being ahigh expanding alloy, the second layer being a low expanding alloy, saidstrip being characterized by a parameter, Aa, which is the differencebetween the thermal c0- efcients of expansion of the two layers, saidparameter having a substantially constant value over a temperature rangeof F. to 300 F. and being in excess of 1.01 l0'I per F. throughout thisrange;

said first layer consisting essentially of nickel, chromium and iron;

said second layer consisting essentially of the following as expressedin percent by weight:

Percent Nickel 30.75-31.75 Cobalt 6.5-8.5 Manganese 0.05-0.5 Carbon0.015-0.l2 Silicon 0.015-0.15

and

Iron Balance 2. A bimetal as set forth in claim 1 wherein the firstlayer consists essentially of 22% chromium, 3% nickel, balance iron.

References Cited UNITED STATES PATENTS 1,604,064 10/1926 Miller 29-l95.51,689,814 10/1928 Brace 29-l95.'5 2,941,882 6/1960 Franklin 75-123HYLAND BIZOT, Primary Examiner gg@ UNITED STATES PATENT OFFICECERTIFICATE OF CORRECTION Patent No. 3 :581,366 Dated June l, 1971Inventor) Arnold Gottlieb and George A. Ma'jesko It is certified thaterror appears in the above-identified patent and that said LettersPatent are hereby corrected as shown below:

Column l, line 34 of the specification (.36Z, by weight) shouldread(36Z, by weght).

Signed and sealed this 21 st day of' December 1 971 (SEAL) Attest:

EDWARD M.FLETGHER,JR3JR. ROBERT GOITSCHALK` Attestng Officer ActingCommissioner of' Patents

